A Two-Step Process of Nitrous Oxide before Carbon Dioxide for Humanely Euthanizing Piglets: On-Farm Trials

Current methods of euthanizing piglets are raising animal welfare concerns. Our experiment used a novel two-step euthanasia method, using nitrous oxide (N2O) for six minutes and then carbon dioxide (CO2) on compromised 0- to 7-day-old piglets. A commercial euthanasia chamber was modified to deliver two euthanasia treatments: the two-step method using N2O then CO2 (N2O treatment) or only CO2 (CO2 treatment). In Experiment 1, 18 piglets were individually euthanized. In Experiment 2, 18 groups of four to six piglets were euthanized. In the N2O treatment, piglets lost posture, indicating the onset of losing consciousness, before going into CO2 where they showed heavy breathing and open-mouth breathing; whereas piglets in the CO2 treatment did not lose posture until after exhibiting these behaviors (p <= 0.004). However, piglets in the N2O treatment took longer to lose posture compared to the CO2 treatment (p < 0.001). Piglets in the N2O treatment displayed more behavioral signs of stress and aversion: squeals/minute (p = 0.004), escape attempts per pig (p = 0.021), and righting responses per pig (p = 0.084) in a group setting. In these regards, it cannot be concluded that euthanizing piglets for 6 min with N2O and then CO2 is more humane than euthanizing with CO2 alone.